I'd invert the question: Rather than seeking to limit the black knights, what can we do to encourage countries to impose sanctions?
In the specific case of Russia, the sanctions regime has been imposed by a huge number of countries. It's caused certain countries, like Monaco and Switzerland, to set aside their historical policy of neutrality. To the extent possible, it's an effective sanctions regime because there are so many allies.
Can we ask China to impose sanctions on Russia? That would be extremely hard to do. China is walking a very fine line of neutrality. It doesn't want to encourage the conflict in Ukraine or destabilize Russia. Nor does it want to sour its relations with the West.
It isn't necessarily about limiting the black knights. We should try to urge other partners to get behind the sanctions.
I'm not sure how well that answers your question.